Splicing of Z-, I-, and M-band titin during development. (A) RT-PCR results with primers spanning exons 7–10 and exons 10–14 in the Z-band, exons 54–56 and exons 66–68 in the I-band, and exons 361–363 in the M-band. (B) Quantification of band density presented for different variants amplified by primers spanning exons 10–14, exons 54–56, and exons 66–68. Significant differences in v4, v6, and v7 ratios were compared in exons 10–14, 54–56, and 66–68 regions, respectively. Mean ± SE (n = 3), * p < 0.05, ** p < 0.01. v, variant; 1–10, different variants. WT, wild type; KO, RNA binding protein 20 (RBM20) knockout. Z, Z-band. I, I-band. M, M-band.